Stabilized rosin esters and hot melt adhesives containing them

Abstract

Improved rosin ester compositions are provided having diminished tendency toward hazing concomitant with good viscosity stability when employed in adhesive systems such as hot melt adhesive systems. Addition of zinc composition to rosin ester formulations in an effective amount serves to secure these improvements. Zinc oxide, zinc hydroxide and zinc salts of organic acids are suitable for employment with zinc resinates being preferred in accordance with the practice of certain embodiments.

What is claimed is: 
     
       1. An improved rosin ester composition comprising a rosin ester and a zinc composition selected from the group consisting of zinc hydroxide, a zinc salt of an organic acid, and mixtures thereof, wherein said zinc composition is present in an amount effective to neutralize a major portion of any acid present in the rosin ester. 
     
     
       2. The composition of claim 1 wherein said zinc composition comprises a zinc salt of an organic acid. 
     
     
       3. The composition of claim 1 wherein said zinc composition comprises zinc resinate. 
     
     
       4. The composition of claim 1 wherein said zinc composition is present in an amount effective to neutralize a major portion of any acid present in the rosin ester to a degree sufficient to impart diminished tendency toward hazing and improved viscosity stability to adhesives comprising said rosin ester composition. 
     
     
       5. The composition of claim 1 wherein said zinc composition is present in an amount effective to neutralize at least seventy-five percent of any acid present in the rosin ester. 
     
     
       6. The composition of claim 1 wherein said zinc composition is present in an amount effective to neutralize substantially all acid present in the rosin ester. 
     
     
       7. The composition of claim 1 wherein said zinc composition is present in an amount in excess of that necessary to effect total neutralization of all acid present in the resin ester. 
     
     
       8. A method for the production of an improved rosin ester composition comprising: (a) providing an esterified rosin; and (b) admixing with said esterified rosin a zinc composition selected from the group consisting of zinc hydroxide, zinc salt of an organic acid, and mixtures thereof; said zinc composition being admixed in an amount effective to neutralize acids present in the esterified rosin to a degree sufficient to impart diminished tendency toward hazing and improved viscosity stability to hot melt adhesives comprising said rosin ester composition. 
     
     
       9. The method of claim 8 wherein said zinc composition comprises a zinc salt of organic acid. 
     
     
       10. The method of claim 8 wherein said zinc composition comprises zinc resinate. 
     
     
       11. The method of claim 8 wherein said zinc composition comprises zinc resinate and said zinc resinate is admixed in an amount effective to neutralize a major portion of any acids present. 
     
     
       12. The method of claim 11 wherein the acids present comprise residual acid catalyst. 
     
     
       13. The method of claim 11 wherein the acids present comprise latent acid catalyst. 
     
     
       14. The method of claim 8 wherein said zinc composition comprises zinc resinate and said zinc resinate is admixed in an amount effective to neutralize at least seventy-five percent of any acids present. 
     
     
       15. The method of claim 8 wherein said zinc composition comprises zinc resinate and said zinc resinate is admixed in an amount effective to neutralize substantially all acids present. 
     
     
       16. An improved tackifier for hot melt adhesives having diminished tendency toward hazing and improved viscosity stability when incorporated in said adhesives, said improved tackifier comprising rosin esterified with polyhydric alcohol and a zinc composition selected from the group consisting of zinc hydroxides, zinc salt of organic acids, and mixtures thereof, wherein said zinc composition is present in an amount effective to neutralize a major portion of any acid present in the rosin ester. 
     
     
       17. A method for improving the physical or chemical properties of rosin ester comprising adding to said ester a zinc composition selected from the group consisting of zinc hydroxide, a zinc salt of organic acids, and mixtures thereof; said zinc composition being admixed in an amount effective to neutralize acids present in the esterified rosin to a degree sufficient to impart diminished tendency toward hazing and improved viscosity stability to hot melt adhesives comprising said rosin ester.